1. Field of the Invention
The subject invention generally pertains to almost any type of HVAC refrigerant system but particularly to PTAC units such as those commonly used for hotel rooms. The invention more specifically pertains to a method of providing such systems with a dehumidification mode without using a reheat coil or relying on a humidistat.
2. Description of Related Art
Refrigerant systems are widely used for heating, cooling and dehumidification of a comfort zone such as a room or other area of a building. Dehumidifying air may simply involve cooling the air below its dew point. Cooling alone, however, can make a room uncomfortably cold. Thus, a heater is sometimes activated to offset the cooling effect, whereby the air can be dehumidified without changing the temperature of the room. The use of a heater while dehumidifying by cooling is known as a reheat process.
The reheat process is applicable to various refrigerant systems; however reheat is not always suitable for Packaged Terminal Air Conditioners/Heat Pumps, also known as PTAC units. PTACs are self-contained refrigerant systems often used for cooling and heating hotel rooms; however, they are also used in a variety of other commercial and residential applications such as apartments, hospitals, nursing homes, schools, and government buildings. Even though PTACs often include an electric heater for a heating mode, energizing a refrigerant compressor for cooling/dehumidifying while energizing an electric heater for reheat would draw a lot of electric current. Such current is not always available due to the often-limited current carrying capacity of the wiring leading to each PTAC unit. Although heavier wiring could be installed, the cost of the higher gage wires would need to be multiplied by the total number of PTAC units of a particular installation. For a hotel with numerous PTAC units, the total cost of the wiring is significant.
Another difficulty of providing a PTAC unit with a dehumidifying mode is that typical dehumidification methods involve the use of a humidity sensor. Examples of such systems are disclosed in U.S. Pat. Nos. 6,892,547; 6,843,068; 6,223,543; 6,070,110; 5,915,473; 5,303,561; 4,735,054; 4,003,729; 3,989,097 and 3,111,010. Although a single humidity sensor may not be that expensive, the total cost can be substantial for installations that include numerous PTAC units.
Other dehumidification schemes are disclosed in U.S. Pat. Nos. 5,743,100 and 4,850,198. The '100 patent provides a refrigerant system with additional dehumidification by continuing to operate the supply air fan for a while after the compressor has been de-energized. Although beneficial, the dehumidification that occurs during the extended but limited run time of the fan may not always be sufficient to meet the total dehumidification needs of the comfort zone. The '198 patent discloses a refrigerant system that reduces humidity by momentarily energizing the cooling system after extended off periods. Although such a system is particularly useful during the night when the cooling demand is low, the system is less valuable during periods of high cooling demand.
Due to the cost and various other drawbacks of current dehumidification methods, there exists a need a dehumidification process that is not only suited for PTAC units but is also applicable to other HVAC systems as well.